A rear projection type display apparatus can comparatively easily produce a large screen display having a reduced size and at a low cost in comparison with a direct sight type CRT, and, therefore, its demand is increasing particularly in North American markets. Unlike a rear projection type display apparatus using a CRT projection tube, a highly fine display without any blur can be produced at peripheral portions of a screen by a dot matrix display, according to a rear projection type display apparatus having a projecting apparatus using a liquid crystal display element of the TN (Twisted Nematic) liquid crystal type or the like as a two-dimensional optical switch element; and, therefore, such a rear projection type display apparatus is expected to find use as a prospective component of a high resolution digital television.
FIG. 11 is a schematic sectional view of a rear rejection type display apparatus, in which a transmission type screen 703 is irradiated with a projected light beam 704 emitted from a projecting apparatus 701 via a mirror 702, and an image is displayed on a front face thereof.
As shown in FIG. 38, the transmission type screen 03 is normally constituted of a Fresnel lens sheet 1402 and a lenticular lens sheet 1401, and the Fresnel lens sheet 1402 is an optical element, which operates similar to a convex lens and has the function of widening the suitable viewing range by bending the direction of the main light beam from the projecting apparatus 701 toward an observer. The lenticular lens 1401 effectively distributes a limited projected light flux from the projecting apparatus 701 to an observing range of the observer to thereby provide a bright image as its object.
FIG. 36 is a schematic sectional view showing an example of a lenticular lens, and FIG. 37 is a schematic perspective view of the lenticular lens.
In the lenticular lens 1401, a plurality of cylindrical lenses 1501 are arrayed in one direction and black stripes 1502 are provided at portions other than portions for condensing a light beam, thereby restraining a reduction in the contrast ratio with regard to an ambient light beam without any loss of the projected light beam ideally by disposing the focal positions of the lenses 1501 on an observing face of the screen.
Generally, by arraying the lenticular lenses such that generators thereof are directed orthogonally to the display face, a wide viewing angle is provided in the horizontal direction. Therefore, a light beam is distributed in the vertical direction only by diffusion produced by a diffusing member blended in a base material of the lenticular lenses or surface portions thereof; and, accordingly, the viewing angle in the vertical direction is considerably narrower than that in the horizontal direction. Further, according to the lenticular lens, lenses having a linear shape are regularly arranged, and, therefore, moire interference fringe is liable to occur on the image.
In contrast thereto, Japanese Unexamined Patent Publication No. 2-77736 discloses a transmission type screen having a constitution in which a transparent base member 1601 is covered with spherical lenses 1602 which are fixed thereto by a transparent resin, as shown in FIG. 39. According to this constitution, no die is used, and therefore, there is no restriction in size in view of fabrication, and a seamless transmission type screen having a large screen surface can be realized. Further, a light beam incident from a side of the spherical lenses is converged by the lens effect of the spherical lenses and is diverged isotropically; and, therefore, wide viewing angles are provided both in the horizontal and vertical directions.
Further, there is a screen having a structure in which optical beads are fixedly attached on a transparent base member via a light-absorbing adhering agent layer, and wherein surfaces of the optical beads on the opposite side of the transparent base member are back-coated transparently, as described in SID94 DIGEST pp. 741-744 (A Novel High-Resolution Ambient-Light-Rejecting Rear-Projection Screen).
Further, Japanese Unexamined Patent Publication No. 9-318801 discloses a plane type lens having a structure in which very small spherical transparent beads are fixed on a transparent base member by a colored hot melt adhering agent layer and a transparent hot melt adhering agent layer. According to this structure, like the structure described in Japanese Unexamined Patent Publication No. 2-77736, due to the lens effect of the beads, the isotropic viewing angles are wide both in the horizontal and vertical directions. Further, an unnecessary light beam incident from outside is absorbed by a light-absorbing adhering agent layer (or colored hot melt adhering agent layer); and, therefore, a high contrast ratio is provided even in a bright environment. Further, high resolution can be realized comparatively easily by reducing the diameter of the bead.
The above-described conventional plane type lens (hereinafter, referred to as a light distribution control element) is fabricated as follows. A flat polyethylene terephthalate (PET)-resin film having a thickness of 120 μm is used as the transparent base member; a transparent adhering agent layer comprising a polyester-based hot melt adhering agent is formed to a thickness of 5 μm on a surface of the resin film; a colored adhering agent layer, in which the same polyester-based hot melt adhering agent is blended with 10 parts by weight of carbon black, is formed on the transparent adhering agent layer; and the entire structure is solidified.
Spherical transparent beads made of glass having a refractive index of 1.935 (wavelength: 589.3 nm) and a diameter of 50 μm are densely arranged so as to be dispersed on the entire surface of the transparent base member. While heating the structure to soften the transparent adhering agent layer and the colored adhering agent layer in a thermostatic chamber, the transparent beads are pressed toward the transparent base member by a pressing plate, to thereby embed the transparent beads in and fixedly adhere them to the colored adhering agent layer and the transparent adhering agent layer. The thickness of the adhering layer after fixation is about 21 μm, including the thicknesses of the transparent adhering agent layer and the colored adhering agent layer, and the transparent beads are exposed from the adhering agent layer by about 58% of the diameter thereof.
When the fabricated light distribution control element. is evaluated as a transmission type screen of a rear projection type display apparatus having a projecting apparatus using a TN type liquid crystal display element as a two-dimensional optical switch element (light bulb), there are provided wide viewing angles equal to or larger than 50 degrees (in this case, an angle giving a brightness half of a front brightness) both in the horizontal direction and the vertical direction, and an unnecessary light beam incident from outside (an observer side) on the light distribution control element is absorbed by the colored adhering agent layer, so that a black display at low brightness can be realized even in a bright environment.
However, when an image projected on the light distribution control element is observed in an oblique direction, it is found that a fringe pattern substantially in the shape of concentric circles emerges and the image quality is significantly deteriorated. Further, it is also found that, when observed in an oblique direction, a change in chromaticity unfavorable to the image is caused.
It is an object of the present invention to provide a light distribution control element that does not produce any deterioration in image quality caused by the occurrence of the above-described fringe pattern, and to provide a display apparatus having high brightness, a high contrast ratio and a high viewing angle using the light distribution control element. Objects other than the above-described object will become more apparent from the following description.